what is the significance of delta H,S,G in thermodynamics

You need to refine your question a bit. Books are written on thermodynamics.

i mean can you explain the reason for the relationship (G = H-TS) and the defn for each

and sponteneity

I searched google.com and found a number of esoteric and highly theoretical discussions about thermodynamics. I know you want basic stuff; I found this one which seems to start from scratch and it appears they keep the math to a minimum. Here it is for you to read. This questions you have asked can not be answered easily on this forum without writing a book. Here is the link. If you want more information I suggest you google it.

http://web.mst.edu/~gbert/basic/thermo.html

ok thanks

Any freshman chemistry text will have good basic discussions also.

In thermodynamics, ΔH (delta H), ΔS (delta S), and ΔG (delta G) refer to changes in enthalpy, entropy, and Gibbs free energy, respectively. They are important concepts that help describe the thermodynamic properties of a system and its reactions.

1. Enthalpy (ΔH):
Enthalpy is a measure of the heat energy absorbed or released during a chemical or physical process at constant pressure. ΔH represents the change in enthalpy between the reactants and products of a reaction. It can indicate whether a reaction is exothermic (ΔH < 0, releasing heat) or endothermic (ΔH > 0, absorbing heat).

To calculate ΔH, you need to know the enthalpy values of the reactants and products. These values can be obtained experimentally using calorimetry or through thermodynamic databases.

2. Entropy (ΔS):
Entropy is a measure of the randomness or disorder in a system. ΔS represents the change in entropy during a process. It can help determine whether a process is spontaneous or non-spontaneous.

To calculate ΔS, you need to consider the difference in entropy between the reactants and products. The change in entropy can be due to changes in molecular configuration, temperature, or phase transitions. You can find the entropy values from tables and databases.

3. Gibbs Free Energy (ΔG):
Gibbs free energy combines both enthalpy and entropy changes to determine the spontaneity and equilibrium of a process. ΔG represents the change in Gibbs free energy during a reaction. It helps predict whether a reaction is energetically favorable (spontaneous) under specific conditions.

The relationship between ΔH, ΔS, and ΔG is given by the equation: ΔG = ΔH - TΔS, where T is the temperature in Kelvin. If ΔG is negative (ΔG < 0), the reaction is spontaneous. If ΔG is positive (ΔG > 0), the reaction is non-spontaneous. If ΔG is zero (ΔG = 0), the system is at equilibrium.

Calculating ΔG requires knowledge of the ΔH and ΔS values, as well as the temperature in Kelvin.

In summary, ΔH indicates the heat absorbed or released, ΔS represents the change in disorder, and ΔG determines the spontaneity of a reaction. These values are crucial for understanding and predicting the behavior of chemical and physical processes in thermodynamics.